Merge pull request #44 from tcdent/claude/dynamic-system-prompts-V7foF

Add mdsh support for dynamic system prompts

Author: tcdent

Cargo.lock

@@ -51,6 +51,9 @@ clap = { version = "4", features = ["derive", "env"], optional = true }
 anyhow = "1"
 thiserror = "2"
 
+# Markdown shell preprocessor (for dynamic system prompts)
+mdsh = { git = "https://github.com/zimbatm/mdsh" }
+
 # Utilities
 fancy-regex = "0.14"
 unicode-width = "0.2"

Cargo.toml

@@ -87,6 +87,34 @@ max_tokens = 8192
 theme = "base16-ocean.dark"
 ```
 
+## Custom System Prompts
+
+You can extend Codey's system prompt by creating `SYSTEM.md` files that are automatically appended to the base prompt. These files are loaded from two locations (in order):
+
+1. **User config**: `~/.config/codey/SYSTEM.md` - personal customizations
+2. **Project**: `.codey/SYSTEM.md` - project-specific instructions
+
+### Dynamic Content with mdsh
+
+SYSTEM.md files support [mdsh](https://github.com/zimbatm/mdsh) syntax, allowing you to embed shell commands that are executed dynamically. This is useful for including context that changes over time.
+
+### Example SYSTEM.md
+
+```markdown
+Today is `$ date '+%d %B %Y'`.
+
+```$
+if which linctl > /dev/null 2>&1; then
+  echo "Use linctl to manage Linear tickets."
+fi
+```
+
+## Guidelines
+- Follow the existing code style
+```
+
+Commands are re-executed on every LLM request, so the prompt always reflects the current state of your environment. Note that this may cause cache invalidation if command output changes between requests.
+
 ## Keybindings
 
 | Key | Action |

README.md

@@ -17,12 +17,12 @@ use ratatui::{
 use tokio::sync::oneshot;
 
 use crate::commands::Command;
-use crate::config::{AgentRuntimeConfig, Config, CODEY_DIR};
+use crate::config::{AgentRuntimeConfig, Config};
 use crate::ide::{Ide, IdeEvent, Nvim};
 use crate::llm::{Agent, AgentId, AgentRegistry, AgentStep, RequestMode};
 #[cfg(feature = "profiling")]
 use crate::{profile_frame, profile_span};
-use crate::prompts::{COMPACTION_PROMPT, SYSTEM_MD_FILENAME, SYSTEM_PROMPT, WELCOME_MESSAGE};
+use crate::prompts::{SystemPrompt, COMPACTION_PROMPT, WELCOME_MESSAGE};
 use crate::tool_filter::ToolFilters;
 use crate::tools::{
     init_agent_context, update_agent_oauth, Effect, ToolCall, ToolDecision, ToolEvent,
@@ -36,34 +36,6 @@ const MIN_FRAME_TIME: Duration = Duration::from_millis(16);
 pub const APP_NAME: &str = "Codey";
 pub const APP_VERSION: &str = env!("CARGO_PKG_VERSION");
 
-/// Build the complete system prompt by appending content from SYSTEM.md files.
-/// Checks (in order):
-/// 1. User config: ~/.config/codey/SYSTEM.md
-/// 2. Project: .codey/SYSTEM.md
-fn build_system_prompt() -> String {
-    let mut prompt = SYSTEM_PROMPT.to_string();
-
-    // Check user config directory: ~/.config/codey/SYSTEM.md
-    if let Some(config_dir) = Config::config_dir() {
-        let user_system_md = config_dir.join(SYSTEM_MD_FILENAME);
-        if let Ok(content) = std::fs::read_to_string(&user_system_md) {
-            tracing::debug!("Appending user SYSTEM.md from {:?}", user_system_md);
-            prompt.push_str("\n\n");
-            prompt.push_str(&content);
-        }
-    }
-
-    // Check project directory: .codey/SYSTEM.md
-    let project_system_md = std::path::Path::new(CODEY_DIR).join(SYSTEM_MD_FILENAME);
-    if let Ok(content) = std::fs::read_to_string(&project_system_md) {
-        tracing::debug!("Appending project SYSTEM.md from {:?}", project_system_md);
-        prompt.push_str("\n\n");
-        prompt.push_str(&content);
-    }
-
-    prompt
-}
-
 /// Result of handling an action
 enum ActionResult {
     NoOp,
@@ -345,9 +317,11 @@ impl App {
             self.oauth.clone(),
         );
 
-        let mut agent = Agent::new(
+        // Use dynamic prompt builder so mdsh commands are re-executed on each LLM call
+        let system_prompt = SystemPrompt::new();
+        let mut agent = Agent::with_dynamic_prompt(
             AgentRuntimeConfig::foreground(&self.config),
-            &build_system_prompt(),
+            Box::new(move || system_prompt.build()),
             self.oauth.clone(),
             self.tool_executor.tools().clone(),
         );

src/app.rs

@@ -153,6 +153,10 @@ impl RequestMode {
     }
 }
 
+/// A function that builds a dynamic system prompt.
+/// Called before each LLM request to allow prompt content to change.
+pub type SystemPromptBuilder = Box<dyn Fn() -> String + Send + Sync>;
+
 /// Agent for handling conversations
 pub struct Agent {
     client: Client,
@@ -163,6 +167,8 @@ pub struct Agent {
     total_usage: Usage,
     /// OAuth credentials for Claude Max (if available)
     oauth: Option<OAuthCredentials>,
+    /// Optional dynamic prompt builder - called before each request
+    system_prompt_builder: Option<SystemPromptBuilder>,
 
     // Streaming state (Some when actively processing)
     state: Option<StreamState>,
@@ -194,6 +200,41 @@ impl Agent {
             system_prompt: system_prompt.to_string(),
             total_usage: Usage::default(),
             oauth,
+            system_prompt_builder: None,
+
+            // Streaming state starts empty
+            state: None,
+            active_stream: None,
+            mode: RequestMode::Normal,
+
+            // Accumulated during streaming
+            streaming_text: String::new(),
+            streaming_tool_calls: Vec::new(),
+            streaming_thinking: Vec::new(),
+            tool_responses: Vec::new(),
+        }
+    }
+
+    /// Create a new agent with a dynamic system prompt builder.
+    ///
+    /// The builder is called before each LLM request, allowing the prompt
+    /// to include dynamic content (e.g., mdsh-processed shell command output).
+    pub fn with_dynamic_prompt(
+        config: AgentRuntimeConfig,
+        prompt_builder: SystemPromptBuilder,
+        oauth: Option<OAuthCredentials>,
+        tools: ToolRegistry,
+    ) -> Self {
+        let system_prompt = prompt_builder();
+        Self {
+            client: Client::default(),
+            config,
+            tools,
+            messages: vec![ChatMessage::system(&system_prompt)],
+            system_prompt,
+            total_usage: Usage::default(),
+            oauth,
+            system_prompt_builder: Some(prompt_builder),
 
             // Streaming state starts empty
             state: None,
@@ -352,6 +393,28 @@ impl Agent {
         self.oauth = oauth;
     }
 
+    /// Refresh the system prompt if a dynamic builder is configured.
+    ///
+    /// This is called before each LLM request to allow the prompt content
+    /// to change (e.g., when mdsh commands return different output).
+    fn refresh_system_prompt(&mut self) {
+        if let Some(ref builder) = self.system_prompt_builder {
+            let new_prompt = builder();
+            if new_prompt != self.system_prompt {
+                debug!(
+                    "System prompt changed ({} -> {} chars)",
+                    self.system_prompt.len(),
+                    new_prompt.len()
+                );
+                self.system_prompt = new_prompt.clone();
+                // Update the first message (system message)
+                if !self.messages.is_empty() {
+                    self.messages[0] = ChatMessage::system(&new_prompt);
+                }
+            }
+        }
+    }
+
     /// Get total usage statistics
     pub fn total_usage(&self) -> Usage {
         self.total_usage
@@ -505,6 +568,9 @@ impl Agent {
             match self.state.as_ref()? {
                 StreamState::NeedsChatRequest => {
                     debug!("Agent state: NeedsChatRequest, clearing streaming data");
+                    // Refresh dynamic system prompt before each request
+                    self.refresh_system_prompt();
+
                     // Clear accumulated streaming data for new request
                     self.streaming_text.clear();
                     self.streaming_tool_calls.clear();

src/llm/agent.rs

@@ -4,5 +4,5 @@ mod agent;
 pub mod background;
 mod registry;
 
-pub use agent::{Agent, AgentStep, RequestMode, Usage};
+pub use agent::{Agent, AgentStep, RequestMode, SystemPromptBuilder, Usage};
 pub use registry::{AgentId, AgentRegistry};